Recently, the importance of lithium (Li) in the industry has been intensifying due to its use in the production of materials of lithium ion batteries or fuels of nuclear fusion reactors. For example, large lithium-ion batteries are used as power supplies of electric vehicles or power storage for smart grids and smart houses. For such uses, techniques for producing Li which serves as a raw material of large lithium-ion batteries at a low cost are required. Meanwhile, in nuclear fusion reactors, tritium which serves as a fuel for nuclear fusion is produced using Li, and thus a large amount of Li is also required in this use.
Li can be extracted from minerals, but is also known to be included in the seawater, and the total amount of Li included in the entire seawater across the globe is massive. Therefore, in a case in which Li can be extracted from the seawater, it is possible to obtain a large amount of Li at a low cost.
Therefore, techniques for recovering Li from an aqueous solution including Li have been proposed. Patent Documents 1 and 2 describes techniques for selectively recovering Li by selectively adsorbing Li (ions) to an adsorbant in the seawater and then desorbing Li from the adsorbent. As the adsorbent, manganese oxide is used in the technique described in Patent Document 1, and a vinyl monomer material is used in the technique described in Patent Document 2.
In addition, Patent Document 3 describes a Li (ion) recovery device in which a lithium ion superconductor having a particularly high ion conductivity of lithium ions (for example, Li1+x+yAlx(Ti, Ge)2−xSiyP3−yO12) is used as a selective permeable membrane that selectively transmits Li ions, a raw liquid (a target liquid from which Li is recovered) and a recovery liquid (a liquid that stores recovered Li) are separated from each other using a structure in which electrodes are provided on both surfaces of the selective permeable membrane, and Li (ions) in the raw liquid is moved in the recovery liquid. In this structure, Li ions can be particularly efficiently recovered at a high selectivity by applying a voltage between both electrodes. Actually, a large amount of Li can be obtained by installing an using Li recovery devices as described above at a specific place (for example, salt lakes in South America) in a large scale.